System and method for transferring natural gas for utilization as a fuel

ABSTRACT

Natural gas is produced when LNG that is contained in an insulated LNG cargo tank(s) of a non-self-propelled LNG carrier (i.e., a barge) evaporates as a result of heat leakage through the walls of the insulated cargo tank(s). The natural gas is transferred from the barge to a tugboat or a towboat that is equipped with natural gas burning engines through a flexible gas transfer assembly so that the tugboat is powered by the natural gas fuel. The pressure in the cargo tank(s) on the barge is, therefore, effectively managed to prevent or substantially reduce the buildup of pressure within the LNG cargo tank(s). The LNG can then be contained within the LNG cargo tank(s) for an appropriate period of time and can be delivered at an appropriate and acceptable equilibrium pressure and temperature.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 13/366,305, filed on Feb. 4, 2012, the contents of which areincorporated herein by reference in their entirety.

FIELD OF THE INVENTION

The present invention generally relates to the transportation of acryogenic liquid such as LNG. More particularly, the present inventionrelates to a system and a method by which a gas provided by theevaporation of a portion of the cryogenic liquid is transferred, in asound operating manner and in compliance with all governinginternational regulations, from the storage tank(s) of a land or marinevehicle for the purpose of being used as fuel by the gas-burning enginesof the another land or marine vehicle.

BACKGROUND OF THE INVENTION

Natural gas, when cooled to approximately −260° F., changes phase from agas to a liquid, thus “Liquefied Natural Gas” or “LNG.” In this phasechange process, the volume required to hold a specific quantity ofnatural gas is reduced by approximately 600 times, thus making itpossible to transport significant, and economic quantities of naturalgas over great distances from source to market.

LNG is a boiling cryogen that is usually stored at atmospherictemperature and pressure equilibrium conditions. Unlike other gaseousfuels such as propane and butane, which can be stored as a liquid atatmospheric temperatures by allowing the liquid and the gas in the tankto reach a stable equilibrium vapor pressure for any given atmospherictemperature, LNG (the principal component of which is methane) cannot bemaintained as a liquid under pressure at atmospheric temperatures due toits low critical point pressure (673+ psia for methane), critical pointtemperature (−115.8° F. for methane), and very high vapor pressures.Accordingly, LNG is stored and is transported in heavily insulatedtanks.

Although the amount of heat that reaches the LNG is significantlyreduced by the tank insulation, the heat inflow to the LNG cannot beentirely eliminated. Consequently, a quantity of cold natural gas vapor(referred to as “boil off vapor” or “boil off”) is constantly beinggenerated and must be removed from the tank and must be either disposedof or re-liquefied in order to prevent an overpressure condition of theLNG tank. Specifically, the resulting boil off is either: (1) vented tothe atmosphere (which venting is limited, by regulation, as anemergency/extraordinary procedure because natural gas is flammable andis a significant greenhouse gas); (2) heated, pressurized, and sent to agas distribution system (in the case of land-based LNG tanks); (3)re-liquefied and returned to the tank as LNG; (4) flared as waste gas;(5) burned in propulsion machinery as fuel (in the case of liquefiednatural gas carriers, or “LNGCs”); or (6) contained in the LNG tank fora finite period of time by allowing the vapor space of the tank toincrease in pressure as the LNG continues to boil. This latter optioncan only be sustained for a relatively short period of time, typicallylimited to days (generally less than a month).

Historically, LNG has been utilized to effect the transportation ofnatural gas from sources in remote regions of the world to end users inpopulation centers where demand for energy, particularly natural gas, iscontinually increasing. LNG has also been utilized for the purpose ofefficiently storing natural gas during periods of low natural gas demandfor later use during periods of high natural gas demand, i.e., so called“peak shaving” operations.

Recently, LNG is increasingly being utilized as a feedstock forgenerating and industrial facilities and as a transportation fuel forboth land and marine vehicles. Natural gas is an attractivetransportation fuel from the perspectives of long term availability,reduced emissions, and cost advantage over traditional distillate fuels.However, to achieve an equivalent energy level, the size of the spaceneeded to house the required quantity of LNG is substantially greaterthan the size of the space needed to house the required quantity of alight distillate fuel, such as diesel fuel.

The increased demand for and use of LNG is creating a need foradditional waterborne strategies for transportation of LNG to end-userdistribution facilities. The marine transportation and distribution ofLNG, whether in inland rivers and waterways or on open ocean coastalroutes, is often most efficiently and economically accomplished bysystems that utilize tugboats and barges.

In the case of the only LNG barge to be built (see Donald W. Oakley,World's First Commercial LNG Barge, OCEAN INDUSTRY, November 1973, at29-32), the LNG boil off was allowed to accumulate in the LNG tank byallowing the pressure in the tank to increase over time. The LNG tanksand the insulation system were designed to contain the boil off for aperiod of 45 days before the LNG tank relief valves would open due tooverpressure, thus releasing the natural gas to the atmosphere.

A significant problem with this approach is that the LNG itself willrise in temperature to reach the equilibrium temperature thatcorresponds to the pressure of the LNG tank. Specifically, as the LNGtank pressure rises, the LNG temperature will also rise. If this warmLNG is then pumped into an LNG storage tank that is at a lower/normalpressure (i.e., a pressure that is slightly above atmospheric pressure,e.g., approximately +100 millibars), the warm LNG will rapidly vaporizeand will release large volumes of cold natural gas as the LNG is cooledby evaporative processes until the LNG again reaches an equilibriumtemperature that corresponds to the new tank pressure. This isunacceptable, since an LNG receiving terminal will be unable to disposeof the excess natural gas and tank overpressure is likely, withsubsequent release of natural gas to the atmosphere. Even a slightlywarmer LNG can be problematic due to the phenomenon of “roll-over”within the storage tank resulting in rapid and uncontrolled LNGvaporization.

There is also an increased safety risk associated with LNG atequilibrium conditions that are above atmospheric pressure should theLNG be accidentally released. At higher pressure equilibrium conditions,the LNG will vaporize at an increased rate, thereby significantlyincreasing thermal radiation risks should the vapor cloud ignite priorto dispersing.

Self-propelled LNGCs use the boil off as propulsion fuel in the ship'sengines and are, therefore, able to maintain proper LNG tank pressureand LNG temperature. In the case of a barge, however, this approach isnot an option because a barge does not have propulsion engines.

The LNG barge referred to above solved this problem of the increasingLNG temperature with time by cooling the LNG in a controlled fashionduring the discharge operation, prior to the LNG being pumped intoland-based tanks. This process was described by Mr. Oakley in theNovember 1973 OCEAN INDUSTRY article and will not be repeated herein.Such cooling process, depending on the length of time that the LNG isaboard the barge and other factors, can result in discharge delays andconsiderable additional expense. It also significantly complicates thedischarging operation. Finally, the added LNG cooling equipment that isrequired is costly to purchase and is expensive to maintain.

U.S. Pat. No. 7,047,899 to Laurilehto et al. teaches the concept ofusing electric generator sets that are fitted to a barge and use naturalgas as fuel, thereby allowing cargo tank boil off to be consumed in theengines, thereby allowing for control of the pressure of the cargotanks. Electrical propulsion power for a tugboat is transferred to thetugboat from the barge by electrical cables. U.S. Patent ApplicationPublication No. 2006/0053806 to Van Tassel also teaches severalapproaches for effectively managing LNG cargo tank boil off and,therefore, LNG cargo tank pressure.

An article entitled LNG-Power Is the Time Now? published in the February2011 issue of MARINE NEWS, teaches the concept of using an LNG fuelbarge combined with a typical inland towboat to provide natural gas fuelto the towboat as there is generally insufficient space on the towboatto house a sufficient quantity of LNG fuel. This article describestransferring LNG to the towboat in liquid, cryogenic form and processingand re-gasifying the liquid gas on the towboat, so that the engines ofthe towboat can make use of the gas as fuel. Such transfer of cryogenicgas is extremely hazardous owing to both the cryogenic temperaturesinvolved and the increased likelihood and consequences of leakage.

FIG. 5 of U.S. Pat. No. 2,795,937 to Sattler et al. (“Sattler”)discloses the transfer of the boil off gas from cargo tanks on a bargeto a tugboat that tows (in this case, pulls) the barge. In FIG. 5,Sattler discloses that the boil off gas is to be transferred from thebarge to the tugboat through a flexible conduit or pipe. The boil offgas is then to be used as fuel in the tugboat's propulsion power plant,in this case a steam boiler, in much the same manner as in aself-propelled ship (e.g., a LNGC). By consuming the boil off in thetugboat's propulsion system, the LNG cargo tank pressure can, therefore,be maintained at near atmospheric pressure.

An examination of Sattler reveals, however, that Sattler fails torecognize the many significant technical, operational, and regulatoryproblems that would prevent the embodiment shown in FIG. 5 from everbecoming operative. (In fact, to the best of the inventor's extensiveknowledge of this field, such an embodiment has never been reduced topractice.) The most significant of these problems is the high likelihoodthat the flexible conduit or pipe would be damaged or severed by theunrestricted relative motion and resulting forces between the barge andtugboat, which is further aggravated by the typical distances (often inexcess of 600 feet) that a barge is towed behind a tugboat. As aconsequence, natural gas would be released to the atmosphere, creating apotentially hazardous situation due to the release of significantquantities of natural gas. At a minimum, this will contribute adverselyto greenhouse gas emissions. Additional problems that Sattler fails torecognize include: (1) the flexible conduit or pipe would have to beable to accommodate motion in all degrees of freedom, as a tugboat andbarge have complete freedom of motion relative to each other; (2)natural gas would be released to the atmosphere when connecting anddisconnecting the flexible conduit or pipe; (3) you would have to find away of purging the flexible conduit or pipe with inert gas prior toconnecting or disconnecting the flexible conduit or pipe; (4) there doesnot appear to be any provision for emergency breakaway and disconnectionof the flexible conduit or pipe should the tugboat need to separate fromthe barge or should the towline part, which is not uncommon; (5) theredoes not appear to be any provision for secondary containment of naturalgas should the flexible conduit or pipe fail or leak; (6) there does notappear to be any provision to detect the leakage of natural gas shouldthe flexible conduit or pipe develop a leak, or to detect leakage at theconnections of the flexible conduit or pipe; and (7) there is noautomatic shutdown of the natural gas transfer from the barge to thetugboat upon failure or leakage of the flexible conduit or pipe or itsconnections.

SUMMARY OF THE INVENTION

It has now been found that the foregoing problems are solved in the formof several separate, but related, aspects. A flexible gas transferassembly is connected using connectors that incorporate self-closingvalves in both halves of the connectors, so that natural gas fuel iscontained within the gas transfer assembly when the assembly isdisconnected, thereby eliminating the need to purge the gas transferassembly with inert gas prior to disconnecting it. Additionally, littleto no natural gas fuel is released to the atmosphere due to theself-sealing nature of the connectors.

In exemplary embodiments, an emergency breakaway connector separates thegas transfer assembly from either a tugboat or a barge, depending on theparticular configuration, should the gas transfer assembly be subject toan excess axial load. (The emergency breakaway connector is designed toseparate at a specific load.) Thus, if the tugboat is required torelease from the barge in an emergency situation, the coupler pins thatconnect the tugboat to the barge are retracted, and the tugboat backsout of the barge notch. The axial load placed on the fuel gas transferassembly as a result of the tugboat exiting the notch causes theemergency breakaway coupling halves to separate, thereby disconnectingthe gas transfer assembly and allowing the tugboat to freely exit thebarge notch. The emergency breakaway connector also incorporatesself-closing valves, trapping any natural gas in the gas transferassembly and preventing release of natural gas.

The gas transfer assembly includes a flexible inner transfer hose and aflexible outer jacket that envelops the inner transfer hose. The jacketspace between the inner transfer hose and the outer jacket is purged andpressurized with a gas that will not support combustion, i.e., an inertgas. The jacket space is maintained at a pressure that is above themaximum pressure of the natural gas fuel in the inner transfer hose. Ifthe inner transfer hose develops a leak, the higher pressure inert gasin the jacket space will leak into the inner transfer hose that carriesthe natural gas fuel. This leakage will result in a drop in the pressurein the jacket space, which will in turn cause a pressure switch to trip,thus providing an alarm and a shutdown signal that secure the transferof the natural gas fuel in a safe manner. Likewise, a leak in the outerjacket will cause the inert gas to leak out, thereby causing a drop inthe pressure in the jacket space and also causing a system shutdown. Inthis manner, any failure of the gas transfer assembly will result in theflow of natural gas fuel being shut down automatically.

In alternative embodiments of the present invention, the gas transferassembly can be replaced with a gas transfer pipe that includes aplurality of pipe segments that are interconnected using swivel jointsto provide the gas transfer pipe with the required flexibility. The pipesegments may be rigid, and the swivel joints may be sealed.

Another potential source of natural gas leakage is the connectors, boththe normal quick connect/disconnect connectors and the emergencybreakaway connectors, that are used to couple the gas transfer assemblyto the tugboat and to the barge. Since natural gas is lighter than airat ambient temperature conditions, leakage of natural gas at theconnectors can be detected by placing hoods or shields over theconnectors and fitting the hoods or shields with gas detector sensors.Even minor leakages of natural gas that would be undetectable by othermeans will be detected by the gas detectors and will cause alarms andsystem shutdowns. The likelihood of a natural gas leak going undetectedand creating a safety issue on the tugboat or the barge is, therefore,reduced to acceptable and manageable levels consistent with the guidingconcepts and principles of the governing international regulations forthese types of vessels.

In alternative embodiments of the present invention, a containment unitcan be fitted closely around the connectors, and air that flows throughvent openings in the containment unit directs any leakage of natural gaswithin the containment unit into a vented space between the inner andouter walls of a double-wall gas pipe which goes to the engine room ofthe tugboat, where a gas detector can detect the leakage and causealarms and system shutdowns.

In accordance with the embodiments of the invention described below,natural gas at ambient temperatures can be transferred from a barge to atugboat in an extremely safe manner. In such application, the fuel bargewith LNG tanks is also fitted with the necessary processing equipment tore-gasify the LNG and heat the resulting natural gas to ambientconditions.

Although the presently preferred embodiments of the present inventiondescribed below are directed to the transfer of natural gas from a bargeto a tugboat, the present invention is not to be understood as beinglimited to marine vessels. It should be understood that the presentinvention applies to any type of vehicle, including but not limited tomarine vessels and land vehicles (e.g., railroad locomotives, railroadcars, and trucks).

BRIEF DESCRIPTION OF THE DRAWINGS

Advantages of the present invention may become apparent to those skilledin the art with the benefit of the following detailed description andupon reference to the accompanying drawings, in which:

FIG. 1 is a profile view of an exemplary articulated tug/barge (“AT/B”)liquefied natural gas carrier (“LNGC”).

FIG. 2 is a plan view of the AT/B LNGC shown in FIG. 1.

FIG. 3 shows an embodiment in accordance with the present invention.

FIG. 4 shows another embodiment in accordance with the presentinvention.

FIG. 5 shows yet another embodiment in accordance with the presentinvention.

FIG. 6 shows an embodiment in accordance with the present invention usedin connection with an AT/B vessel in which the tug is pitched at zerodegrees in relation to the level trim of the barge.

FIG. 6A shows an embodiment in accordance with the present inventionused in connection with an AT/B vessel in which the tug is pitched at anextreme aft pitch in relation to the level trim of the barge.

FIG. 6B shows an embodiment in accordance with the present inventionused in connection with an AT/B vessel in which the tug is pitched at anextreme forward pitch in relation to the level trim of the barge.

FIG. 7 shows detail of the limits of motion of a natural gas flexiblehose in accordance with the present invention.

FIG. 8 shows an exemplary embodiment in accordance with the presentinvention in the context of an arrangement of an inland towboat and anatural gas fuel barge.

FIG. 9 shows another exemplary embodiment in accordance with the presentinvention in the context of an arrangement of a railroad locomotive anda natural gas fuel tender car.

FIG. 10 shows a fuel gas transfer pipe in accordance with the presentinvention.

FIG. 11 shows detail of the limits of motion of a fuel gas transfer pipein accordance with the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Definitions of certain terms used in this specification are as follows:

Vehicle—any means in or by which something is carried or conveyed; ameans of conveyance or transport. As used herein, the term “vehicle”includes but is not limited to marine vessels (e.g., ships, tugboats,towboats, barges, and articulated tug/barges (“AT/Bs”)) and landvehicles (e.g., railroad locomotives, railroad cars, and trucks).

Self-propelled vessel—a marine vessel that possesses permanentlyinstalled capability to propel itself at sea, i.e., a “ship.”

Non-self-propelled vessel—a marine vessel that is without a permanentlyinstalled capability to propel itself at sea, i.e., a “barge.” A“self-propelled” vessel that, for whatever reason, is not using itsinstalled capability for propulsion is not, as defined herein, a“non-self-propelled” vessel.

LNG—liquefied natural gas.

LNGC—a self-propelled LNG carrier of ship form.

LNG Barge—a non-self-propelled LNG carrier.

AT/B—a vessel arranged in an articulated tug/barge configuration,wherein propulsion of a non-self-propelled barge is provided by aseparate tugboat that is connected to the barge by a pinnedconnection(s) that restrict motion in all degrees of freedom except forpitch.

AT/B LNGC—an LNG carrier arranged in an articulated tug/barge (AT/B)configuration, wherein propulsion of the barge is provided by a separatetug that is connected to the barge by a pinned connection(s) thatrestrict motion in all degrees of freedom except for pitch.

Towboat—an inland river vessel arranged for pushing barges on inlandwaterways and rivers.

Referring to FIGS. 1 and 2, an exemplary AT/B LNGC is formed bycombining a barge portion 1 with a tugboat portion 2. The barge 1 andtugboat 2 are coupled together with coupling pins 3 such that relativemotion is restricted in all degrees of freedom except for pitch. In theAT/B LNGC shown in FIGS. 1 and 2, the barge 1 includes one or more LNGcargo tanks 4 for storing LNG cargo during transport. As shown in FIG.2, the barge 1 has four LNG cargo tanks. However, it should beunderstood that the number and size of the cargo tanks included in thebarge 1 in no way limits the scope of the invention as defined in theappended claims.

FIG. 3 illustrates an exemplary embodiment in which ambient temperaturenatural gas (i.e., the boil off from the LNG stored in the cargo tanks 4of the barge 1) is transferred from a supply source 17 from the LNG fuelsystem on the barge 1 through a fuel gas transfer assembly 5 to thesupply piping 18 for the natural gas fuel system of the tugboat 2, wherethe natural gas will be used as the vessel fuel for the natural gasfueled engines that power the tugboat 2.

In accordance with an embodiment of the present invention, a fuel gastransfer assembly 5 includes a flexible gas transfer assembly that issuitable for handling ambient temperature natural gas (e.g., LNG boiloff) at the required pressure and is suitable for the specificenvironment in which it is used (e.g., a marine environment). The fuelgas transfer assembly 5 includes a flexible inner transfer hose 6 thatis enveloped by a flexible outer jacket 7. In a preferred embodiment,the inner transfer hose 6 is a stainless steel, corrugated hose (i.e., aBellows hose). In alternative embodiments, the inner transfer hose 6 maybe made of other materials, including regular steel, aluminum, orwire-reinforced rubber, and it should be understood that the materialfrom which the flexible inner transfer hose 6 is made in no way limitsthe scope of the invention as defined in the appended claims. The innertransfer hose 6 need not even be a hose, but can be any means oftransferring the natural gas that is flexible and is compatible with therequired LNG pressures and with the surrounding environment.

In accordance with an embodiment of the present invention, a jacketspace 30 between the outer jacket 7 and the inner transfer hose 6 isfilled with a gas that does not support combustion in the event thatnatural gas leaks into the jacket space 30 from the inner transfer hose6. In a preferred embodiment, the jacket space 30 is filled with aninert gas, preferably nitrogen. However, in alternative embodiments, thejacket space 30 can be filled with other gases that will not supportcombustion, including but not limited to carbon dioxide, argon, orhelium. Here again, the choice of the particular gas that fills thejacket space 30 in no way limits the scope of the invention as definedin the appended claims.

In accordance with an embodiment of the present invention, the inert gasthat fills the jacket space 30 is held at a pressure that is higher thanthe maximum pressure of the natural gas that is within the innertransfer hose 6. The inert gas is admitted to the jacket space 30 of thefuel gas transfer assembly 5 through a connection 9 located at one endof the fuel gas transfer assembly 5. A purge connection 8 is provided atthe other end of the fuel gas transfer assembly 5 and can be opened toallow the atmosphere within the jacket space 30 to be completely filledwith inert gas. Once purging is complete, the purge connection 9 isclosed and the pressure within the jacket space 30 is maintained at apressure that is above the pressure of the natural gas contained withinthe inner transfer hose 6. In an exemplary embodiment, the maximumpressure of the natural gas that is within the inner transfer hose 6 istypically 5 bars, and the jacket space 30 is held at a pressure of 6bars.

In a preferred embodiment, the inert gas, such as nitrogen, is providedfrom an inert gas source 13 to the fuel gas transfer assembly 5 througha supply line 31 and the connection 9. A pressure reducing valve 12 isprovided in the supply line 31 to deliver the inert gas to the jacketspace 30 at the desired pressure. Additionally, the pressure reducingvalve 12 can optionally use a feedback loop 32 to monitor the pressurein the inner transfer hose 6 so as to maintain the desired pressuredifferential between the inner transfer hose 6 and the outer jacket 7 inthe jacket space 30. A flow restrictor 11 is fitted to limit the flowrate of the inert gas to the jacket space 30 to ensure that the pressurein the jacket space 30 drops should a leak develop. A pressure switch 10is fitted to monitor the pressure of the inert gas in the supply line31. If this pressure drops below a predetermined limit, the pressureswitch 10 closes, initiating a shutdown signal to terminate the flow ofnatural gas as well as sounding an alarm to alert operating personnel.

In accordance with an embodiment of the present invention, the fuel gastransfer assembly 5 provides an increased level of safety by ensuringthat a leak in the inner transfer hose 6 is captured within the outerjacket 7, while simultaneously providing for the shutdown of thetransfer of the natural gas fuel from the barge to the tugboat andconcomitantly sounding an alarm. Should a leak develop in the innertransfer hose 6, the higher pressure of the inert gas that fills thejacket space 30 between the inner transfer hose 6 and the outer jacket 7will leak into the inner transfer hose 6. Consequently, the pressure ofthe inert gas in the supply line 31 will drop, which in turn will causethe pressure switch 10 to close. In a preferred embodiment, the closingof the pressure switch 10 triggers both the generation of warning alarmsignals and a shutdown signal that shuts down the supply of natural gasfuel by closing master gas valves. In an exemplary embodiment, theshutdown signal that is triggered by the closing of the pressure switch10 ties into the emergency shutdown system of the barge 1 to close themaster gas valves of barge 1. Further, the outer jacket 7 prevents anyrelease of natural gas to the surrounding atmosphere. Similarly, a lossof pressure in the jacket space 30 could occur due to a failure of theouter jacket 7 or a loss of inert gas supply. In any case, a systemshutdown will be triggered, ensuring the required level of safety.

In accordance with an embodiment of the present invention, aself-sealing emergency breakaway coupling 14 is fitted to allow thetugboat 2 to exit from the coupling notch of the barge 1 (see FIGS. 1and 2) in an emergency situation. Normally the inner transfer hose 6would be disconnected from the tugboat 2 by releasing a self-sealingquick connect/disconnect connector 15 from the self-sealing matingconnection 16 on the tugboat 2. In a preferred embodiment, the emergencybreakaway coupling 14 is fitted with self-closing valves (not shown) onboth halves of the coupling 14. The coupling 14 is maintained in thenormal connected condition by breakaway bolts (not shown) such that whenabnormal loads are put on the fuel gas transfer assembly 5, such aswould be experienced when the tugboat 2 pulls away from the barge 1 inan emergency without first releasing the fuel gas transfer assembly 5,the bolts break at a prescribed load, thereby allowing the halves of thecoupling 14 to separate and the internal self-sealing valves of thecoupling 14 to close. By closing, the self-sealing valves prevent anyrelease of natural gas to the atmosphere. Other forms of emergencybreakaway couplings could be employed without limiting the scope of thepresent invention.

In accordance with an embodiment of the present invention, partialshields 19 are fitted over the quick connect/disconnect assembly 15 andthe mating connection 16 on the tugboat 2, and over the emergencybreakaway coupling 14 on the barge 1. In a preferred embodiment, eachpartial shield 19 can be moved to provide access to the couplingsunderneath (i.e., the quick connect/disconnect connector 15 and themating connection 16, and the emergency breakaway coupling 14) so as notto interfere or inhibit the emergency disconnection of the fuel gastransfer assembly 5. This result can be accomplished by any number ofmeans that are well known to those having ordinary skill in the art,including but not limited to providing the partial shield 19 with ahinge or similar means.

Since the natural gas fuel is at an ambient temperature, it is lighterthan air. Therefore, any leakage of the natural gas fuel from the innertransfer hose 6 will rise and will be captured by the partial shield 19in such a manner that a gas detector 20 located within the partialshield 19 will sense the presence of natural gas before flammableconcentrations of the natural gas can accumulate. Upon detection of thenatural gas fuel, the gas detector 20 generates a system shutdown signalthat is used to cause the flow of the natural gas fuel to be stopped,the fuel system to be put in a safe condition, and an alarm to besounded. Since the partial shield 19 will concentrate any natural gasfuel at the gas detector 20, any leakage of natural gas fuel willinitiate a system shutdown and an audible alarm.

FIG. 4 shows an alternative to the embodiment shown in FIG. 3. In thealternative embodiment shown in FIG. 4, the emergency breakaway coupling14 is located on the tugboat 2, adjacent to the mating connection 16 andthe quick connect/disconnect connector 15 fitted to the fuel gastransfer assembly 5. By locating the emergency breakaway coupling 14 onthe tugboat 2, credible leak sources can be concentrated on the tugboat2, and the number of partial shields 19 and gas detectors 20 can bereduced to one each versus two each, as illustrated in the embodimentshown in FIG. 3.

FIG. 5 shows an alternative to the embodiment shown in FIG. 4. In theembodiment shown in FIG. 5, a containment unit 33 is fitted closelyaround the emergency breakaway coupling 14, the quick connect/disconnectassembly 15, and the mating connection 16. In a preferred embodiment, acover 34 of the containment unit 33 can be opened to provide access tothe couplings underneath (i.e., the emergency breakaway coupling 14, thequick connect/disconnect connector 15, and the mating connection 16) soas not to interfere or inhibit the emergency disconnection of the fuelgas transfer assembly 5. This result can be accomplished by any numberof means, including but not limited to attaching the cover 34 to thecontainment unit 33 with a hinge or similar means. Containment unit 33also includes vent openings 35 which allow air to flow through thecontainment unit 33 in the direction indicated by the arrows shown inFIG. 5.

In operation, due to the close fit of the containment unit 33 around theemergency breakaway coupling 14, the quick connect/disconnect assembly15, and the mating connection 16, the air flowing through the ventopenings 35 directs any leakage of natural gas within the containmentunit 33 into a vented space 36 between the inner and outer walls of thedouble-wall gas pipe 18 which goes to the engine room of the tugboat 2.Consequently, since the vented space 36 typically has a gas detector(not shown) disposed therein, it is less likely that a natural gas leakfrom the emergency breakaway coupling 14, the quick connect/disconnectassembly 15, and/or the mating connection 16 would go undetected.

Containment unit 33 further includes a support block 37 which surroundsand supports the fuel gas transfer assembly 5. In an advantageous aspectof the present embodiment, the support block 37 enables a cleanerbreakaway of the fuel gas transfer assembly 5 from the barge 1 in theevent of an emergency separation, since the movement of the fuel gastransfer assembly 5 as it exits the containment unit 33 will beconstrained by the surrounding support block 37.

FIGS. 6, 6A, and 6B illustrate an embodiment in accordance with thepresent invention in which the fuel gas transfer assembly 5 is used inan AT/B LNGC of the type shown in FIGS. 1 and 2. As shown in FIG. 6, anAT/B tugboat 2 is coupled to a barge 1 using an AT/B coupler connection,where the reference numeral 3 refers to both the AT/B coupler connectionand to the pivot center of the coupling connection. In accordance withan embodiment of the present invention, the fuel gas transfer assembly 5is flexible and can thus flex within its allowable limits. The fuel gastransfer assembly 5 is supported by a fixed radius saddle 21 to ensurethat the minimum allowable bend radius of the fuel gas transfer assembly5 is not violated.

FIG. 6 specifically illustrates the implementation of the fuel gastransfer assembly 5 that is illustrated in FIG. 4, wherein the emergencybreakaway coupling 14 is located adjacent to the quickconnect/disconnect connector 15 and the mating connection 16 on thetugboat 2. This should not be considered limiting in any way, as thearrangement illustrated in FIG. 3 could alternatively be employed.Although omitted from FIG. 6 for the sake of clarity, it will beunderstood that the partial shield 19 and the gas detector 20 can beused with the emergency breakaway coupling 14, the quickconnect/disconnect connector 15, and the mating connection 16 in themanner shown in FIG. 4. Likewise, the containment unit 33 can be usedwith the emergency breakaway coupling 14, the quick connect/disconnectconnector 15, and the mating connection 16 in the manner shown in FIG.5. In addition, FIG. 6 (as well as FIGS. 6A and 6B that follow) does notshow a termination for the supply source 17 on the barge 1, since it isto be understood that the supply source 17 terminates wherever the LNGfuel happens to be located on the barge.

FIG. 6A illustrates the embodiment shown in FIG. 6, with the tugboat 2pitched at five degrees aft in relation to the level trim of the barge1. This represents a typical extreme aft pitch of the tugboat 2, whichcan occur as a result of normal at-sea movement of the tugboat 2relative to the barge 1 in pitch due to the effect of ocean waveconditions, and illustrates the ability of the fuel gas transferassembly 5 to accommodate the movement between the tugboat 2 and thebarge 1.

FIG. 6B illustrates the embodiment shown in FIG. 6, with the tugboat 2pitched at five degrees forward in relation to the level trim of thebarge 1. This represents a typical extreme forward pitch of the tugboat2, which can occur as a result of normal at-sea movement of the tugboat2 relative to the barge 1 in pitch due to the effect of ocean waveconditions, and illustrates the ability of the fuel gas transferassembly 5 to accommodate the movement between the tugboat 2 and thebarge 1.

FIG. 7 is a composite view of the fuel gas transfer assembly 5 showingthe extreme limits of its movement due to the pitching of the tugboat 2relative to the barge 1. Reference numeral 3 indicates the center ofrotation of the AT/B coupler in pitch (see FIGS. 6, 6A, and 6B). Thefuel gas transfer assembly 5 is supported by the fixed radius saddle 21,which is fitted on the barge 1 to ensure that the minimum allowable bendradius of the fuel gas transfer assembly 5 is not violated. A similarfixed radius hose saddle 22 is fitted on the tugboat 2, also to ensurethat the minimum allowable bend radius of the fuel gas transfer assembly5 is not violated. The extreme forward pitch of the tugboat 2 relativeto the barge 1 is indicated by position 24. The extreme aft pitch of thetugboat 2 relative to the barge 1 is indicated by position 25. The zeropitch of the tugboat 2 relative to the barge 1 is indicated by position23.

FIG. 8 illustrates a towboat 26 (i.e., an inland river push-modetugboat) that pushes an LNG fuel barge 27 as part of a flotilla of cargobarges of various types, in accordance with another embodiment of thepresent invention. As shown in FIG. 8, natural gas fuel is transferredfrom the LNG fuel barge 27 to the towboat 26 in the manner describedhereinabove, wherein the fuel gas transfer assembly 5, the natural gassupply line 17 from the natural gas supply on the barge 27, the naturalgas supply line 18 to the natural gas-fueled engines on the towboat 26,the emergency breakaway connector 14, the quick connect/disconnectconnector 15, and the mating connection 16 are fitted on the towboat 26and the barge 27 in the manner illustrated and described hereinabove.

FIG. 9 illustrates another embodiment in accordance with the presentinvention, in which a railroad locomotive is powered by ambienttemperature natural gas fuel (e.g., LNG boil off) that is provided froma tender car 29. As shown in FIG. 9, natural gas fuel is transferredfrom the tender car 29 to the locomotive 28 in the manner describedhereinabove, wherein the fuel gas transfer assembly 5, the natural gassupply line 17 from the natural gas supply on the tender car 29, thenatural gas supply line 18 to the natural gas-fueled engines on thelocomotive 28, the emergency breakaway connector 14, the quickconnect/disconnect connector 15, and the mating connection 16 are fittedon the locomotive 28 and the tender car 29 in the manner illustrated anddescribed hereinabove.

In alternative embodiments in accordance with the present invention, anarticulated fuel gas transfer pipe can replace the fuel gas transferassembly 5 in the foregoing embodiments. As shown in FIG. 10, anexemplary fuel gas transfer pipe 38 has several pipe segments 39, 41,43, 45, 47 which are interconnected by swivel joints 40, 42, 44, 46. Inpreferred embodiments, the pipe segments of fuel gas transfer pipe 38are rigid, and thus the fuel gas transfer pipe 38 is a rigid pipebetween the swivel joints. In further preferred embodiments, the swiveljoints of fuel gas transfer pipe 38 are double sealed. The space (notshown) between the inner seal, which primarily seals in the natural gas,and the outer seal is filled with nitrogen or other inert gas and ismaintained at a pressure above the pressure of the natural gas containedwithin the gas transfer pipe 38. The nitrogen pressure is monitored inthe same fashion as is shown in FIG. 4, such that any leakage of theseals is immediately detected and the transfer of natural gas isshutdown.

In an exemplary embodiment, the fuel gas transfer pipe 38 is used in anAT/B LNGC of the type shown in FIGS. 1 and 2. Referring to FIG. 6, anAT/B tugboat 2 is coupled to a barge 1 using an AT/B coupler connection,where the reference numeral 3 refers to both the AT/B coupler connectionand to the pivot center of the coupling connection. In accordance withan aspect of the present invention, the swivel joints 40, 42, 44, 4provide the fuel gas transfer pipe 38 with flexibility so that it canflex within its allowable limits when coupled between the barge 1 andtugboat 2.

FIG. 11 is a composite view of the fuel gas transfer assembly 38 showingthe extreme limits of its range of motion due to the pitching of thetugboat 2 relative to the barge 1. Reference numeral 3 indicates thecenter of rotation of the AT/B coupler in pitch (see FIGS. 6, 6A, and6B). The extreme forward pitch of the tugboat 2 relative to the barge 1is indicated by position 48. The extreme aft pitch of the tugboat 2relative to the barge 1 is indicated by position 49. The zero pitch ofthe tugboat 2 relative to the barge 1 is indicated by position 50.

While this invention has been described in conjunction with exemplaryembodiments outlined above and illustrated in the drawings, it isevident that many alternatives, modifications and variations will beapparent to those skilled in the art. Accordingly, the exemplaryembodiments of the invention, as set forth above, are intended to beillustrative, not limiting, and the spirit and scope of the presentinvention is to be construed broadly and limited only by the appendedclaims, and not by the foregoing specification. Without limiting thegenerality of the foregoing, those skilled in the art will appreciatethat the embodiments in accordance with the present invention are notlimited to the transfer of LNG and include and encompass the transfer ofother cryogenic liquid gases.

What is claimed is:
 1. A system for transferring natural gas, the systemcomprising: a barge; a tugboat positioned within a notch of the bargeand coupled to the barge with a pin connection to push the barge,wherein a relative pitch motion between the tugboat and the barge spansa range of +5 to −5 degrees of relative pitch; an articulated pipehaving a first end through which natural gas is transferred from thebarge and a second end; and at least one coupling coupled to the secondend of the articulated pipe and through which the natural gas istransferred to the tugboat.
 2. The system of claim 1, wherein thearticulated pipe comprises a plurality of pipe segments interconnectedby at least one swivel joint.
 3. The system of claim 2, wherein each oneof said plurality of pipe segments is rigid.
 4. The system of claim 2,wherein the at least one swivel joint has at least one seal.
 5. Thesystem of claim 4, wherein the at least one swivel joint comprises aninner seal and an outer seal.
 6. The system of claim 5, wherein theinner seal seals the natural gas in the swivel joint.
 7. The system ofclaim 5, wherein a space between the inner seal and the outer seal isfilled with a gas that will not support combustion.
 8. The system ofclaim 7, wherein the gas that will not support combustion comprises aninert gas.
 9. The system of claim 8, wherein the inert gas comprisesnitrogen.
 10. The system of claim 7, further comprising: a supply linethrough which the gas that will not support combustion is supplied tothe space between the inner seal and the outer seal; and a pressureswitch that monitors the pressure of the gas that will not supportcombustion in the supply line.
 11. The system of claim 10, wherein thepressure switch closes when the pressure of the gas that will notsupport combustion in the supply line drops.
 12. The system of claim 11,further comprising an alarm system coupled to the pressure switch. 13.The system of claim 12, wherein the closing of the pressure switchcauses an alarm to be triggered.
 14. The system of claim 13, furthercomprising a shutdown system coupled to the pressure switch.
 15. Thesystem of claim 14, wherein the closing of the pressure switch causesthe shutdown system to shut down the supply of the natural gas to thearticulated pipe.
 16. The system of claim 7, wherein a space between theinner seal and the outer seal is at a pressure that is greater than thepressure of the natural gas within the articulated pipe.
 17. The systemof claim 1, wherein the at least one coupling comprises a self-sealingbreakaway connection through which the second end of the articulatedpipe is coupled to the tugboat, wherein the breakaway connectionautomatically breaks upon application of an excessive load withoutreleasing the natural gas from the articulated pipe.
 18. The system ofclaim 1, wherein the at least one coupling comprises a self-sealingconnection through which the articulated pipe is coupled to the tugboat,such that the articulated pipe can be intentionally disconnected withoutreleasing natural gas.
 19. The system of claim 1, wherein the bargecomprises a non-self-propelled LNG carrier.
 20. A system fortransferring natural gas, the system comprising: a barge; a tugboatpositioned within a notch of the barge and coupled to the barge with apin connection to push the barge, wherein a relative pitch motionbetween the tugboat and the barge spans a range of +5 to −5 degrees ofrelative pitch; an articulated pipe through which natural gas istransferred from the barge to the tugboat; at least one coupling throughwhich the natural gas is transferred from the articulated pipe to thetugboat; and a containment unit disposed around the at least onecoupling to contain a leak of the natural gas from the at least onecoupling.
 21. The system of claim 20, wherein the containment unit isfitted closely around the at least one coupling.
 22. The system of claim20, wherein the containment unit has at least one opening through whichair can flow.
 23. The system of claim 22, wherein air flows within thecontainment unit in a direction from the barge to the tugboat.
 24. Thesystem of claim 23, wherein the air flow directs natural gas leakagefrom the at least one coupling toward the tugboat.
 25. The system ofclaim 20, wherein the containment unit comprises a support blockdisposed around the articulated pipe.
 26. An articulated conduit systemfor transferring fluid between two vessels, the system comprising: aplurality of rigid conduits interconnected by at least four swiveljoints that are configured to permit positional alterations of theconduits that result from relative pitch motion between a first vesseland a second vessel, wherein the system is configured to be secured at afirst end on the first vessel and at a second end on the second vessel,and the relative pitch motion spans a range of +5 to −5 degrees ofrelative pitch.
 27. The articulated conduit system of claim 26, whereinthe first and second vessels are a tugboat and a barge.
 28. Thearticulated conduit system of claim 27, wherein the tugboat and thebarge are configured as an articulated tugboat and barge, wherein thetugboat is configured to push the barge through a pin connection. 29.The articulated conduit system of claim 26, wherein each of the at leastfour swivel joints is configured to provide a gas-tight seal.
 30. Thearticulated conduit system of claim 26, wherein each of the at leastfour swivel joints is configured to provide a gas-tight seal forcontaining a gas within the conduit system with a pressure that isgreater than a pressure of the gas contained within the conduit system.31. The articulated conduit system of claim 26, having four swiveljoints.
 32. The articulated conduit system of claim 27, comprising atleast one swivel joint rotatable about a transverse axis relative to thetugboat and the barge to accommodate pitch motion between the tugboatand the barge.
 33. The articulated conduit system of claim 27,comprising at least three swivel joints rotatable about longitudinal ortransverse axes relative to the tugboat and the barge, wherein the atleast three swivel joints are rotatable together to accommodatedisplacement in a vertical direction relative to the tugboat and thebarge.
 34. The articulated conduit system of claim 27, comprising atleast one swivel joint rotatable about a vertical axis relative to thetugboat and the barge to accommodate pitch motion between the tugboatand the barge.
 35. The articulated conduit system of claim 26, whereinthe plurality of conduits comprise pipe segments.
 36. The articulatedconduit system of claim 26, wherein the first vessel is a tugboat havinga natural gas fuel system and the conduit system is in fluidcommunication with a supply pipe for the natural gas fuel system. 37.The articulated conduit system of claim 36, wherein the second vessel isa barge having a supply of natural gas and the conduit system is influid communication with the supply of natural gas.